Swivel shackle assemblies have been used for many years in conjunction with cables and a hoist to lift and move heavy objects about the workplace, such as dies, molds, heavy castings, etc. These swivel shackle assemblies typically include a "U" shaped shackle member that is pivotal on a swivel body that in turn is rotatable about an axis on a base that is perpendicular to the swivel axis of the shackle on the base. This enables the shackle to accommodate two axes pivotal movement which is necessary for the geometry of the hoist arrangement.
In a typical hoist arrangement, an overhead crane has a depending single cable that is tied to four(more or less) outwardly extending cables connected to the shackle assemblies. Each shackle assembly typically has a threaded fastener extending centrally there-through that bolts the shackle directly to the top surface of the die or mold.
There have been found to be several problems associated with these prior shackle assemblies that we have observed over many years of manufacturing and testing these shackles. The first is that the "U" shaped shackle member that includes generally spaced parallel legs that are pinned at their ends to the swivel body, tend to spread apart after either extensive use, or sometimes upon overloading. To our knowledge no solution has, prior to the present invention, been devised for either ameliorating or eliminating this very fundamental problem.
A second problem results in the improper design of the hoisting arrangement by the hoist operator or his assistants. As noted above, each of the shackles is tied to a single hoist cable by an angularly related branch cable, and it can be simply shown that the load on each of the shackles is proportional to the angle of the shackle branch cables to a vertical axis. That is, as the angle of the shackle branch cable increases with respect to the vertical axis, the load on the shackle increases for a pre-determined load mass, which of course is a vertical load. To our knowledge, none of the shackle assemblies previously devised has provided the operator with any warning or indication as to an unsafe angle on the shackle member, that may cause failure of the shackle assembly.
The following patents are representative of the prior art relating to dual axis hoist shackle assemblies.
The Andrewe, et al., U.S. Pat. No. 3,297,293, issued Jan. 10, 1967; the Tsui, et al., U.S. Pat. No. 4,705,422, issued Nov. 10, 1987; and the Chandler, U.S. Pat. No. 5,352,056, issued Oct. 4, 1994, all show swivel shackle assemblies having a "U" shaped member or shackle that is pinned to a rotary swivel member by transverse pins that are separate from the "U" member itself. In this design, it is necessary to fix these shackle pins in the swivel body, and this design is particularly prone to "U" members spreading either as a result of long term fatigue or overloading.
A second group of patents represented by the Wong, et al., U.S. Pat. No. 4,570,987, issued Feb. 18, 1996; the Tsui, et al., U.S. Pat. No. 4,641,986, issued Feb. 10, 1987; and the Tsui, U.S. Pat. No. 5,405,210, issued Apr. 11, 1995, show hoist swivel shackle assemblies in which the ends of the "U" shaped shackle extend radially inwardly and form the pivotal bosses for the shackle on the swivel body member. This design somewhat reduces the long term loading problem on the shackle discussed above, but it does not significantly minimize that problem.
Furthermore, in none of the prior swivel shackle assemblies discussed above is there any provision for a device that indicates to the operator when an excessive shackle angle is placed on the shackle causing a potentially hazardous condition.
It is a primary object of the present invention to ameliorate the problems noted above in hoist swivel shackle assemblies.